In various sectors of industry, it is important to have especially pure substance streams available. Catalytic chemical reactions are one example. Catalysts are often very sensitive to poisoning. Thus, even exceptionally small quantities of impurities in the starting material stream can collect on the catalyst and poison it. Typically, for olefin polymerization reactions on modern catalysts, for example metallocene catalysts, olefin streams are required which comprise not more than a few ppb (parts per billion, i.e. 10−9 parts) of impurities per part of the desired substance (“polymer-grade” olefins). Olefins deriving from typical olefin sources (steam cracker, fluid catalytic cracker, dehydrations, MTO (“methanol to olefins”) processes mostly have very much higher contents (ppm or even per-mille range) of impurities such as carbon monoxide or oxygen (“chemical grade”); these contents must be decreased appropriately before use for polymerization.
Typically, the substance streams to be purified are air, nitrogen or argon or hydro-carbons such as ethylene, propylene, 1-butene, 2-butene, 1,3-butadiene or styrene. Typical impurities which must as a rule be removed are oxygen and carbon monoxide, and often also water, carbon dioxide, hydrogen or even sulfur, arsenic or antimony compounds. Processes for the removal of such impurities from substance streams are known.
Many adsorptive processes and adsorbents for the removal of carbon monoxide from substance streams are known. The German laid-open specification DE 1 929 977 teaches catalysts comprising 20 to 60 parts of CuO to 100 parts of ZnO and the use thereof for the removal of CO from ethylene and propylene streams at a temperature in the range from 50 to 200° C. U.S. Pat. No. 3,676,516 teaches a supported Cu catalyst, whereof 20 to 95% of the copper is present as Cu2+, and the use thereof for CO removal from ethylene or propylene streams at a temperature below about 200° C., and in the examples specifically at about 93° C. U.S. Pat. No. 4,917,711 discloses an adsorbent which comprises a copper compound on a high-surface-area support, but also adsorbs olefins and hence is only suitable for the purification of nitrogen, inert gases and saturated hydrocarbons.
WO 95/021146 A1 teaches a process for the removal of carbon monoxide and also arsine, if present, from liquid hydrocarbon streams by contacting with a sorbent which, depending on the embodiment, comprises dispersed copper at the oxidation levels 0, +1 or +2, and in certain cases also manganese dioxide. EP 537 628 A1 discloses a process for the removal of carbon monoxide from alpha olefins and saturated hydrocarbons by contacting with a catalyst system based on at least one oxide of a metal selected from Cu, Fe, Ni, Co, Pt and Pd and at least one oxide of a metal selected from groups 5, 6 or 7 of the periodic table of the elements at 0 to 150° C. U.S. Pat. No. 4,713,090 describes an adsorbent for obtaining high-purity carbon monoxide by pressure or temperature swing adsorption. The adsorbent comprises a composite support with a core of silicon or aluminum oxide and an outer layer of an activated charcoal on which a copper compound is supported.
WO 2004/022223 A2 teaches a copper-, zinc-, zirconium- and optionally aluminum-comprising adsorption composition and the use thereof for the removal of CO from substance streams in the completely reduced state.
Processes are also known for activating or reactivating catalysts, also those comprising copper, or passivating them for transport. DD 0 153 761 relates to a process for the activation or reactivation of iron molybdate redox catalysts, which can also comprise copper, wherein the catalysts are first calcined in a non-oxidizing atmosphere and then brought into contact with an oxidizing gas. DE 199 63 441 A1 teaches a process for the regeneration of copper-comprising hydrogenation catalysts by first oxidizing and then reducing treatment, wherein the reduction is preferably first performed in the hydrogenation reactor. WO 02/068 119 A1 discloses copper-comprising hydrogenation and dehydrogenation catalysts which are used in the reduced state and are passivated for transport by partial oxidation of the copper. EP 296 734 A1 describes copper-comprising shift or methanol catalysts which owing to reduction at a temperature below 250° C. have a Cu surface area of at least 70 m2/g based on copper.
WO 2007/093526 discloses a copper, zinc and zirconium oxide-comprising adsorption composition, where the copper-comprising fraction thereof has a reduction level, expressed as the weight ratio of metallic copper to the sum of metallic copper and copper oxides, calculated as CuO, of at least 45% and at most 75%, and a process for the removal of carbon monoxide from carbon monoxide-comprising substance streams by adsorption on this adsorption composition. An adsorption composition with a reduction level in the stated range is supposed to be especially regenerable.
WO 2007/093526 also discloses a process for the production of the adsorption composition by:    a) preparation of a solution of the components of the adsorption composition and/or of soluble starting compounds for these;    b) precipitation of a solid from this solution by addition of a base;    c) separation and drying of the solid;    d) optionally a calcination of the solid;    e) shaping of the solid into shaped bodies; and    f) optionally a calcination of the shaped bodies;    g) adjustment of the reduction level of the copper-comprising fraction of the adsorption composition to a value of at least 45% and at most 75%.
During this, after the complete reduction with hydrogen, the reduction level is adjusted to the desired value by oxidation of the adsorption composition precursor. During this, the residual hydrogen present is flushed from the reaction vessel with nitrogen, the desired oxidation temperature is set and a small proportion of oxygen is mixed into the nitrogen stream.
Depending on the selected adsorber size, the maximum uptake capacity of the adsorption composition for carbon monoxide comprised therein is sooner or later reached, so that it must be regenerated.
WO 2007/093526 also discloses the regeneration of the copper, zinc and zirconium oxide-comprising adsorption composition after the use thereof for the adsorptive removal of carbon monoxide from carbon monoxide-comprising substance streams by passing an inert gas such as for example nitrogen, methane or argon over the adsorption composition at a temperature of preferably at least 150° C. and at most 400° C. WO 2007/093526 also discloses the addition of oxygen in traces, in general in a proportion of at least 1 ppm, preferably at least 5 ppm and particularly preferably at least 10 ppm, in general at most 300 ppm, preferably at most 250 ppm and particularly preferably 200 ppm to the inert gas, preferably nitrogen or argon.
During the regeneration, the reduction level of the copper-comprising fraction of the adsorption composition can increase. However, at very high reduction levels, for example of 85%, a further rise in the reduction level can lead to an abrupt fall in the uptake capacity of the adsorption composition for CO. Particularly with multiple regeneration the danger exists that a certain critical reduction level will be exceeded and the uptake capacity of the adsorption composition falls.
An excessively low reduction level also has an adverse effect on the uptake capacity of the adsorption compositions for carbon monoxide. At a reduction level of <50%, the uptake capacity is already markedly lowered and is now only ca. 40% of the uptake capacity at a reduction level of 70%.